8 oo Kemp . —On the Question of the Occurrence of 
however, to be due merely to a slightly more rapid occurrence of the 
processes which cause that disappearance in the young tap-roots used in 
the experiments described above. Also in a few lateral roots which were 
examined, although no tetraploid figures were to be seen in the extreme • 
tip, in one instance, at any rate, such a cell was found at the point of 
exit from the tap-root. It seems probable, therefore, that search at this 
point would reveal a certain number of the tetraploid cells, relapsed into 
comparative inactivity and therefore inconspicuous and likely to escape 
notice. 
It was pointed out earlier that there is a certain difficulty in tracing the 
fate of the tetraploid cells, owing to the variety of their points of origin and 
to the difficulty of ascertaining their rate of division. Although such cells 
are seen near the growing point after a comparatively prolonged period of 
regrowth, yet their number at that point does slowly diminish. The 
hypothesis of heterotype reduction of the chromatin would seem to have 
been sufficiently disproved above. Therefore, either the activity of division 
of the tetraploid cells is so much lessened that they pass out of the zone of 
active growth, without giving rise to the rows of cells of like tetraploid 
nature, which they would normally produce, or they break down rapidly 
and are absorbed by the neighbouring cells. Probably both processes are 
in action. It has been stated by Gerassimow that the increase in size of 
a cell is correlated with a decrease in its rate of division. In apparent 
accordance with this statement, large tetraploid cells are found, generally 
singly, sometimes in twos or threes, but never in extensive rows, at the 
growing point. Further, not many disintegration figures are to be seen at 
the latter, these occurring generally further back. Multipolar division occurs 
to a considerable extent throughout the entire root-tip. 
From the occurrence then of the multipolar divisions, fragmentation and 
disintegration figures described, and also of certain abnormally large cells 
far back from the growing point, it may be inferred that the tetraploid 
cells either break up into several smaller individuals with something 
approaching the normal amount of chromatin, or disintegrate, or pass over 
into the permanent tissue in accordance with Nemec’s second hypothesis. 
It seems clear that, at any rate in the root tissues of the plants examined 
in these experiments, heterotype reduction does not play a part in the 
disappearance of the tetraploid cells; that on the contrary, their nuclei, instead 
of reverting to any such automatic process, tend to break up by one or other 
of the above methods. From the nature of the figures observed, it would 
appear that this breaking up is due ultimately, as suggested by Strasburger, 
to a lack of sufficient centripetal force to hold together so large a mass of 
chromatin as is contained in these nuclei. 
